1. Field of the Invention
The present invention relates generally to the use of a plurality of positive drive units that are operated in unison to feed a plurality of strands of material such as yarn along an array of feed paths to a workstation at a uniform feed rate that can be controlled independently of a selected speed at which the array of feed paths is being rotated about a center axis that extends through the workstation. More particularly, the present invention relates to a system for reliably, continuously and uniformly feeding a plurality of strands such as yarn to the knitter head of a high speed knitter by utilizing positive drive units that are arranged in an array that extends about a center axis of the knitter head's workstation to assist in defining a set of strand feed paths that is rotatable at a selected first speed of rotation about the center axis together with a bank of strand supply packages, with the positive drive units having capstans about which the strands are wrapped, and with the capstans being rotated in unison at a second speed of rotation that can be selected independently from the first speed of rotation to pay out stands from their supply packages and to deliver the payed out strands to the workstation at a desired uniform feed rate and at a uniform tension that is isolated from variations in strand tension that occur as strands are payed out from their supply packages, even in the presence of relatively high centrifugal force and windage loads.
2. Prior Art
In the conventional manufacture of reinforced hose of the type used to transport high pressure fluid, one well known process begins with the formation of an "inner tube" or tubular "core" portion of the hose from a material such as rubber. The core is fed lengthwise along a path of travel that extends centrally through what is referred to as the "knitter head" of a knitter machine. As core portions move continuously through the knitter head, a plurality of cam operated knitter needles carry out a series of relative movements to knit strands of material such as yarn to form a tautly fitting web or jacket of reinforcing material about the outer surface of the core.
An additional layer of "outer tube" or "cover" material such as rubber usually is extruded to extend about the strand-reinforced core. In some instances, the covered, strand-reinforced core is again fed through a knitter to apply still another knitted layer or jacket of reinforcing material, whereafter still another layer of cover material such as rubber usually is applied. If rubber is the material that is being used to form the core and cover layers, the covered hose is put through a curing process to complete its manufacture.
The strands that are knitted by the knitter head to form a knitted jacket of reinforcing material at the workstation of the knitter typically include a dozen or more strands of yarn that each are fed along separate feed paths to the workstation from separate supply packages. Suitable guides of various forms are used to define the feed paths, with some guide formations being more complexly configured than others, but with all of the guides being configured to be as readily "threadable" as possible inasmuch as time spent "threading" or "rethreading" a knitter to replace an exhausted yarn supply package or to replace a broken strand of yarn represents machine "down time" that can seriously limit productivity. In the operation of a knitter, minimizing machine "down time" is an objective that probably is second in importance only to the objective of assuring that the strands are properly fed to and knitted by the knitter head so that a product of high quality is produced.
To feed strands of material along an array of feed paths from supply packages to a knitter head, it is necessary to apply sufficient tension to the strands to cause them to pay out from their supply packages and to move along their threaded feed paths. Many knitters rely solely on the cyclic movement of the knitter needles to provide such tension. However, this approach has a number of drawbacks.
One disadvantage that results from utilizing the needles of a knitter to effect the tensioning and feeding of strands from supply packages to a knitter head is that, on average, the tension force that a knitter needle must apply to pay out yarn from its supply package and feed it along a properly threaded feed path is greater than is compatible with the important additional objective of maximizing the service life of the needles and associated components such as the cams and guide members that cooperate with the needles to cause proper needle movement to take place so that a desired knit pattern can be produced with regularity and without waste.
Another disadvantage that results from using the needles of a knitter to effect strand tensioning and feeding is that, as each strand of yarn is fed along its associated feed path, the tension that is experienced by the strand as it pays out from its supply package varies considerably. The extent to which strands tends to resist being payed out from their supply packages and being fed along their threaded feed paths varies erratically from moment to moment, whereby the extremes in magnitude and the rapid variations in magnitude of the tension forces to which the various needles of a knitter are subjected cause undue wear and breakage of knitter components, and can greatly diminish productivity by adding to machine "down time" that is needed to carry out maintenance, repair and rethreading to replace broken strands.
From the viewpoint of providing a high quality product, the uneven feeding of yarn that results from the presence of erratic strand tension forces and uneven strand feeding causes some strand portions to be pulled more tightly than others as the strands are being knitted by the knitter head, with the result being an uneven application of the knitted layer of reinforcing material which can diminish the capability of the resulting hose to properly withstand the transmission therethrough of pressurized fluid for an appropriately lengthy service life. In some instances, variations and distortions appear in the knit pattern that are so significant as to be unacceptable.
Due to the detrimental effects caused by variations in strand tension and strand feed rate, and inasmuch as these detrimental effects tend to become more pronounced the faster that a knitter is operated, the speed at which knitters can be operated continuously and reliably often has had to be slowed to a far greater degree than is desired if good knitter productivity is to be maintained. If too high a speed of production of reinforced hose is attempted, needle breakage, strand breakage and resulting "down time" needed to repair and maintain the knitter, and to replace broken needles and strands is found to diminish rather than to enhance productivity.
While a number of desirable types of knit patterns can be formed in reinforcing material by utilizing a knitter head that does not rotate about a center axis along which a hose core travels as it moves centrally through the knitter head, there are some desirable knit patterns that can be implemented only if there is rotary movement of the knitter head relative to the core as the core moves centrally through the knitter head. Helical knit patterns, for example, can only be produced if relative rotary movement takes place between the knitter head and the core as the core moves centrally through the knitter head.
Because it is almost always impractical, if not impossible, to effect such relative rotary movement by rotating the core about the center axis of the knitter head, the needed relative rotation usually must be obtained by rotating the knitter head and its attendant strand supply and guide system components about a central axis along which the core is fed as it travels centrally through the knitter head. Especially in continuous hose manufacturing processes wherein non-rotatable extrusion equipment is used to form a hose core that is fed to a knitter located downstream from where the core has emerged from the extruder, the only viable option available for producing a helical knit pattern is to rotate the knitter head and its attendant strand supply and guide system components about the path that is followed by the core as it travels centrally through the knitter head.
Rotating the knitter head and its associated strand supply and guide components presents a number of concerns that need to be addressed with care if desirable knitter performance and reasonable productivity are to be obtained. The speed of rotation of strand guide and supply system components and strand feedpaths about the center axis that needs to be achieved if good productivity is to be obtained is desirably in excess of 600 revolutions per minute, with rotational speeds of 600 to 1400 revolutions per minute being preferred. As rotational speed is and the speed at which hose core material is fed through the workstation are increased, the rate at which knitter needles execute their stroke-like cycles of movement also must be increased to more rapidly implement the knitting function they perform.
At supply system rotation speeds of 600 to 1400 revolutions per minute, the knitter needles preferably are operated at a correspondingly high speed that is within the range of about 3000 to about 6000 strokes per minute. However, with previously proposed strand supply and guide system proposals, the desirably high productivity that theoretically can be obtained if rotation of the supply system is increased to within the range of about 600 to about 1400 revolutions per minute has not been attainable, much less maintainable for reasonable lengths of time. The principal limiting factor that has stood as an obstacle has been an inability to suitably feed a rotating array of strands to the knitter head so that a needle stroke rate of between about 3000 to about 6000 strokes per minute not only can be attained but also maintained for lengthy production runs. The erratic tensioning and uneven feeding of strands of yarn to the needles of the knitter has stood as a barrier both due to resulting breakage of needles and strands, and due to the excessive wear and tear that is inflicted on the needles and their associated cam and guide components.
Among the problems that need to be taken into account if knitter heads and their attendant strand supply and guide components are rotated at speeds that are even as high as about 600 revolutions per minute are the resulting centrifugal force and windage loadings that are imposed on not only on the components of the knitter but also on reaches of strand material as they extend along their prescribed feed paths. If the problems that are generated by centrifugal force and windage loadings are added to the problems that are generated by erratic tensioning and uneven feeding of strands to the knitter head, excessive component wear and breakage as well as excessive strand breakage tend to result. Moreover, if proper high speed knitter operation is attempted by also increasing the rate of movement of the knitter needles above about 1000 strokes per minute to somewhere within the range of about 3000 to about 6000 strokes per minute, the problems that stem from erratic tensioning and uneven feeding of strands to the knitter head are exacerbated, with the result being that almost no meaningfully lengthy production runs can be carried out between incidents of "down time" that require machine repair and/or replacement of broken strands. Furthermore, the quality of the resulting product has tended to be unacceptable due to variations and distortions that appear in the knit pattern.
In efforts to overcome the detrimental effects that result if knitter needles, acting alone, are used to pay out strands from supply packages and to feed the strands through guides to the workstation of a knitting machine, a variety of supplemental feeding devices have been proposed that are intended to be installed along strand feed paths to assist knitter needles in tensioning and feeding strands. However, 1) because the operation of a set of supplemental feeding devices must be carefully coordinated to ensure that the strands are fed in unison (i.e., at substantially identical feed rates) to the knitter head, and 2) because the uniform feed rate at which the strands are fed needs to properly accommodate the rate at which the knitter head makes use of strand material to knit a web of reinforcing material about a hose core, proposed supplemental feeding devices typically are relatively complex and expensive.
To the extent that supplemental feeding devices for use with an array of strands being fed to the workstation of a knitter have been proposed, most of the proposals employ components that have not been found to preform reliably and with good longevity of service life in the presence of the significant centrifugal and windage force loadings that result if a knitter head and its strand supply, guide and feed system are rotated at speeds of even as much as 600 revolutions per minute. If rotational speed of supply system components is increased to the more desirable range of about 600 to about 1400 revolutions per minute which is preferred in order to obtain good productivity from a high speed knitter, components and strand reaches that are spaced only a few inches from the axis of rotation easily can be subjected to loadings of force that are hundreds of times their weight. In such circumstances, electrical switch components and the like often are found to develop malfunctions and/or fail to perform as intended. Likewise, it is not unusual to find that even simple mechanical devices that employ relatively movable parts and have proven to be highly reliable when used in stationary environments malfunction and/or fail to perform as intended when subjected to an environment of high speed rotation.
Despite the existence of a longstanding need for a highly reliable system for driving and coordinating the operation of an array of supplemental feeding devices that are installed along a rotating array of strand feed paths to appropriately reduce the tension forces that strands exert on knitter needles, no suitably simple and reliable mechanical, electrical or electro-mechanical system has been proposed to meet this need. While the desirability has been recognized of providing a knitter that can be continuously and reliably operated at relatively high speeds of supply system component rotation that typically are in the range of about 600 to 1400 revolutions per minute with knitter needle stroke rates being maintained within the range of about 3000 to about 6000 per minute, a limiting factor that has stood squarely in the path of the provision of such a machine is the need for a strand supply, guide and feeding system that will function reliably, despite being subjected to significant centrifugal force and windage loadings, to effect controlled feeding, in unison, of a rotating array of strands of reinforcing material to the needles of a knitter head so that the needles can precisely and consistently implement a selected knit pattern as a web of reinforcing material is formed about a hose core that is traveling at relatively high speed through the workstation of the machine.